1. Field of the Invention
The invention relates to fuel burning furnaces and, more particularly, to a fuel burning furnace having improved characteristics of heat circulation, heat transfer, and, in general, energy efficiency.
2. Description of the Prior Art
Rising fuel costs and depleted fuel supplies have been a serious problem of recent times. These problems have initiated a nationwide concern for the energy efficiency of our fuel burning products. Among the products which use considerable amounts of fuel to operate are the furnaces which heat our homes and offices. While prior art furnaces do serve to provide heat to our living quarters they have done so in a relatively inefficient and wasteful manner.
Most prior fuel burning furnaces constitute box-type structures with several major openings including an inlet for air to be heated, an outlet for heated air, and an outlet for combustion gases. The furnaces additionally contain a heat exchanger for extracting heat from hot combustion gases and for containing spent fuel fumes, burners and a pilot to ignite and convert the fuel to energy, and a blower to force air to be heated through the heat exchanger and outwardly to areas to be heated.
Prior gas furnaces, although effective to produce heat, are not entirely satisfactory from an energy efficiency viewpoint. Much of the inefficiency inherent in furnaces of present design stems from the poor heat transfer characteristics of the heat exchangers. These heat exchangers generally provide a series of heat exchange enclosures, each one housing a burner, arranged in side-by-side relation. The burners are located near the bottom of the heat exchange enclosure and hot combustion gases are allowed to rise through the enclosure, thus heating the interior walls so that heat may be transferred to the exterior surfaces over which air to be heated is passed. A problem with these heat exchangers is that hot combustion gases pass essentially unrestricted up through the enclosure and out the flue vent, thus wasting large quantities of heat which could otherwise be extracted from the flue gases. Since much of the heat which could be utilized is lost through the flue vent and chimney, more fuel must be burned to provide the requisite heating air.
Another problem not adequately addressed by prior furnaces relates to providing the burners with sufficient fresh air to complete combustion of the fuel being burnt. During the winter months, when the furnaces are used the most, it is a standard practice to keep the house as air-tight as possible to prevent warm air from escaping and to provide a good insulating effect. This creates a problem, however, in that an adequate supply of fresh air is not allowed to enter the house. Fresh air is necessary to complete the combustion process and to extract all the potential energy provided by the combustible fuel. If complete combustion does not occur, a significant amount of the combustion fuel will be vented along with the hot combustion gases. As a result of this incomplete burning of fuel, additional fuel must be burned to compensate for the inefficiency of the furnace and provide the requisite heat necessary to maintain proper temperature levels.
Recent proposals have provided electric ignition systems to ignite the fuel at the burners when the temperature drops below a predetermined level. It has been suggested that electric ignition systems are more energy efficient than the gas pilot systems presently utilized, as they are not continually burning and are only activated on command from a remote temperature sensor. These electrical ignition systems have suffered from several drawbacks. In spite of the fact that they are not continually operating, as is the case with the standard gas pilots, their overall efficiency is very poor, on the order of about 30%. Another problem which occurs from the use of electric ignition is that each time at the beginning of combustion cycle when the furnace burners have come on, water vapor is permitted to condense on surfaces of the heat exchanger because the electric ignition does not dry it off. This water tends to corrode the heat exchangers and shorten their life. Even more importantly, corrosion reduces the heat transfer characteristics of the heat exchanger, since a layer of rust develops on the outer surfaces on the heat exchange enclosures.
Yet another problem which has not been adequately addressed relates to the detection of problems of heat flow and air circulation in the furnace. Prior furnaces provide no means of checking the efficiency or operation of the furnace, thus making it very difficult to detect and correct problems at an early stage. As problems with air circulation and heat transfer develop, the furnace must burn more fuel in order to maintain adequate room temperatures. For instance, if the heat transfer characteristics of the heat exchanger were to fall to 50% of their normal operating values, the furnace would burn twice as much fuel to compensate for this problem with no indication that a problem even existed, and what is worse, no way to even check. Thus, problems may go undetected for long periods of time with nothing being done to correct them.